Composition for clear gas barrier laminates

ABSTRACT

Scrap material having both a thermoplastic polyurethane and a copolymer of ethylene and vinyl alcohol is recycled by blending the scrap material into a thermoplastic polyurethane composition and preparing a barrier membrane from the blended material. The virgin thermoplastic polyurethane and the thermoplastic polyurethane of the scrap material are polymerized using at least about 60 percent by weight, based on the weight of the polyurethane produced, of a polyester diol having a weight average molecular weight of at least about 500 and having from four to five carbon atoms between substantially all of the ester [—O—C(═O)—] groups. The blend material containing the virgin thermoplastic urethane and the scrap material is formed into a layer of a barrier membrane. The resulting membrane has a haze of no more than about 12%.

FIELD OF THE INVENTION

[0001] This invention concerns methods for making clear barriermembranes for cushioning devices for shoes. In particular, the inventionrelates to transparent, resilient laminate membranes including athermoplastic polyurethane elastomer.

BACKGROUND OF THE INVENTION

[0002] Barrier membranes and inflatable bladders formed from suchmembranes have been used in footwear. It is often desirable to usethermoplastic polymeric materials to form the membranes becausethermoplastic materials may be reclaimed and reformed into new articles,reducing waste during manufacturing operations and promoting recyclingof scrap. Barrier membranes for inflated bladders can thus be made witha thermoplastic barrier layer. Thermoplastic polymeric barrier layermaterials typically form crystalline regions or spherulites that serveto make the egress of fluid molecules through the layer more difficult.

[0003] Thermoplastic polymeric barrier materials with at a thicknessadequate to provide the desired low gas transmission rate [GTR]generally do not have a low enough modulus for cushioning in shoesbecause the inflated bladder is subjected to high strains during use. Inorder to overcome this problem, the barrier materials have been blendedor layered with elastic materials. Elastic materials, or elastomers, areable to substantially recover their original shape and size afterremoval of a deforming force, even when the part has undergonesignificant deformation. Elastomers may likewise be thermoplastic, andso a flexible, thermoplastic barrier film may be formed with acombination of thermoplastic elastomers and thermoplastic barrier layermaterials.

[0004] In footwear, styling considerations have made low haze,transparent barrier membranes desirable. A blend material may be cloudyor hazy, however, if the materials blended together in a layer are notentirely compatible. A related problem arises in recycling scrapmembrane material. When a membrane has been constructed with layers ofdifferent materials, those materials are not easily separated in thescrap. Consequently, the multi-layer scrap must be blended into one oranother of the layer materials for recycling. For the desired clarity tobe preserved in the blended layer, the multi-layer scrap material mustbe compatible with the layer material into which it is blended.

[0005] One type of thermoplastic elastomer that has been blended orlayered with the barrier materials to make resilient membranes isthermoplastic polyurethane. Membranes including a first layer of athermoplastic polyurethane, and a second layer including a barriermaterial, such as a copolymer of ethylene and vinyl alcohol, aredescribed, for example, in U.S. Pat. No. 6,082,025, issued Jul. 4, 2000;U.S. Pat. No. 6,013,340, issued Jan. 11, 2000; U.S. Pat. No. 5,952,065,issued Sep. 14, 1999; and U.S. Pat. No. 5, 713,141, issued Feb. 3, 1998,each of which is incorporated herein by reference. Although membraneswith separate layers of the thermoplastic polyurethane material and thepolymeric barrier material have had acceptable clarity, recycling scrapmulti-layer membrane material by blending the scrap material into one ofthe layers has been problematic. In particular, the blended layer andmembrane have noticeably lower reduced clarity because ofincompatibility of the blended materials.

[0006] Thus, it would be desirable to have a transparent, multi-layermembrane in which the layer compositions are compatible so thatincorporation of the multi-layer scrap into one layer of the membranedoes not result in undesirable haziness.

SUMMARY OF THE INVENTION

[0007] The present invention provides an article of footwear in whichthe sole includes a visible, fluid-containing bladder. To be visible, atleast a part of the bladder wall forms at least a part of an exteriorportion of the sole. The bladder wall comprises a laminate membranehaving low haze. The laminate membrane includes at least a first layercontaining a polyurethane and a copolymer of ethylene and vinyl alcohol,and a second layer containing a copolymer of ethylene and vinyl alcohol.The polyurethane includes at least about 50 mole percent, based on thetotal moles of hydroxyl-functional reactants used to produce thepolyurethane, of a polyester diol having a weight average molecularweight of at least about 500 and having a linear alkylene group havingfrom two to about six carbon atoms between substantially all of theester groups.

[0008] The invention further provides a method of manufacturingfootwear, in which a laminate membrane is prepared with at least a firstlayer containing a polyurethane and a copolymer of ethylene and vinylalcohol, and a second layer containing the copolymer of ethylene andvinyl alcohol. Again, the polyurethane includes at least about 50 molepercent, based on the total moles of hydroxyl-functional reactants usedto produce the polyurethane, of a polyester diol having a weight averagemolecular weight of at least about 500 and having a linear alkylenegroup having from two to about six carbon atoms between substantiallyall of the ester groups. The blend of polyurethane and copolymer ofethylene and vinyl alcohol in the first layer is made by includingrecycled material of the polyurethane and copolymer of ethylene andvinyl alcohol in the layer, especially along with virgin material thatincludes at least the polyurethane. The recycled material has a firstlayer including the copolymer of ethylene and vinyl alcohol and a secondlayer including thermoplastic polyurethane material. Because of theparticular polyurethane used, the blended material is very low in haze.The low haze is desirable for the aesthetic design of the footwear. Thelow haze membrane can be colorless or colored with dye or transparentpigment to provide a low haze colored membrane. The bladder may befilled with a colorless or colored fluid.

[0009] The membrane preferably includes the layer of blended material asan outer membrane layer in a multi-laminar structure. The transparentmembrane of the article also preferably includes a barrier layer toprevent the transfer of fluid from one side of the membrane to theother, preferably with a thermoplastic elastomer layer between the layerof the blended material and the barrier layer. Such durable, elastomericbarrier membranes may be used to prepare inflated bladders. By “durable”it is meant that the membrane has excellent resistance to fatiguefailure, which means that the membrane can undergo repeated flexingand/or deformation and recover without cracking and without delaminationalong the layer interfaces or cracking through the thickness of themembrane, preferably over a broad range of temperatures. For purposes ofthis invention, the term “membrane” is used to denote a free-standingfilm separating a fluid, preferably a gas at higher than atmosphericpressure, from the atmosphere outside of the article of footwear. Filmsthat are wholly laminated or painted onto another article for purposesother than separating fluids, e.g., coatings, are excluded from thepresent definition of a membrane.

[0010] The layer of blended material of the invention has a low haze, bywhich is meant a haze of no more than about 12%, preferably no more thanabout 5%. Haze may be measured according to ASTM D-1003.

[0011] The transparent membrane is part of a bladder containing a fluid.The bladder may be inflated with a gas such as nitrogen, air, or asupergas. The term “supergas” refers to a large molecule gas that has alow solubility coefficient, such as SF₆, CF₄, C₂F₆, C₃F₈, and so onwhich are described in Rudy, U.S. Pat. Nos. 4,183,156 and 4,287,250, andRudy et al., U.S. Pat. No. 4,340,626, incorporated herein by reference.A portion of the transparent membrane of the enclosure or bladder forms,or is visible through, at least part of an exterior wall of the articleof footwear into which the bladder is incorporated.

[0012] The barrier membrane preferably has a gas transmission rate thatis sufficiently low to allow the bladder to remain “permanently” sealedand inflated, that is, to retain a useful internal pressure for theuseful life of the article into which it is incorporated. An acceptedmethod for measuring the relative permeance, permeability, and diffusionof different film materials is ASTM D-1434-82-V. The gas transmissionrate of a membrane is expressed at the quantity of gas per area per timethat diffuses through the membrane. The gas transmission rate may beexpressed in units of (cc)(mil)/(m²)(24 hours), at standard temperatureand pressure. The gas transmission rate of the barrier membrane providedby the invention is preferably less than about 1(cc)(20 mils)/(m²)(24hours).

BRIEF DESCRIPTION OF THE DRAWINGS

[0013] The present invention will become more fully understood from thedetailed description and the accompanying drawing, wherein:

[0014]FIG. 1 shows a side view of an article of footwear according tothe invention.

DETAILED DESCRIPTION OF THE INVENTION

[0015] Referring to FIG. 1, there is shown a shoe 100 having an upper110 and a sole 120 attached to the upper 110. The upper 110 can beformed form a variety of conventional materials including, but notlimited to, leathers, vinyls, nylons, and other generally wovenmaterials. The sole 120 includes a midsole 122 and an outsole 124. Abladder 200 containing a fluid, preferably a gas, is disposed in themidsole 122 to provide cushioning support to the foot.

[0016] Bladder 200 has as its walls a transparent, laminate membrane,which as shown in FIG. 1, forms at least a part of the exterior of sole120. The transparent membrane has a first layer including a blend of athermoplastic polyurethane and a copolymer of ethylene and vinyl alcoholand a second layer including a copolymer of ethylene and vinyl alcohol.The blend of the thermoplastic polyurethane and the copolymer ofethylene and vinyl alcohol has a low haze, preferably a haze of no morethan about 12%, more preferably no more than about 5%. The compositionof the blended first layer allows the bladder to have a desirable“crystal clear” appearance.

[0017] The thermoplastic polyurethane is polymerized from at least about50 mole percent, preferably at least about 62 mole percent, morepreferably at least about 65 mole percent, and yet more preferably atleast about 69 mole percent of a polyester diol, the mole percent beingbased on the total moles of hydroxyl-functional reactants used toproduce the polyurethane.

[0018] The polyester diol has linear alkylene groups having from two toabout six carbon atoms between substantially all of the ester groups. By“substantially all” it is meant that not more than about 5 mole percent,preferably not more than about 2 mole percent, and most preferably none,of the alkylene groups between the ester groups have less than two ormore than about six carbon atoms. The polyester can be prepared fromdiols of from two to six carbon atoms reacted with dicarboxylic acidshaving four to six carbon atoms and/or epsilon-caprolactone.Accordingly, the polyester diol may be prepared by reaction of one ormore diols selected from ethylene glycol, 1,3-propanediol,1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol and combinations ofthese with one or more dicarboxylic acids selected from succinic acid,glutaric acid, adipic acid, anhydrides of these acids, and combinationsthereof or with epsilon-caprolactone.

[0019] In a particularly preferred embodiment, the polyester diol ispoly(epsilon-caprolactone) diol. Polyesters of epsilon-caprolactone maybe prepared by initiating the self-condensation of the lactone withwater or a diol, such as ethylene glycol, 1,3-propanediol,1,4-butanediol, and so on. A lactone-based polyester diol may also beprepared by reacting the lactone with the hydroxyl groups of a polyesterdiol prepared from one or more of the dicarboxylic acids and one or morediols, as already described. In a preferred embodiment, the polyesterdiol is a poly(epsilon-caprolactone) diol with a weight averagemolecular weight of from about 1500 to about 3000, preferably about 1800to about 2500.

[0020] The polyester diol preferably has a weight average molecularweight of at least about 500, more preferably at least about 1000, andeven more preferably at least about 1800. The polyester diol may have aweight average molecular weight of up to about 10,000, but polyesterdiols having weight average molecular weight of up to about 5000,especially up to about 4000, are preferred. The polyester dioladvantageously has a weight average molecular weight in the range fromabout 500 to about 10,000, preferably from about 1000 to about 5000, andmore preferably from about 1500 to about 4000. The weight averagemolecular weights may be determined by ASTM D-4274.

[0021] The polyester polyol-based polyurethanes are formed by reactionof the polyester diol with at least one diisocyanate and, preferably,one or more extender compounds (also called chain extension agents)having two isocyanate-reactive functional groups. The diisocyanate maybe selected from aromatic, aliphatic, and cycloaliphatic diisocyanatesand combinations thereof. Representatives of useful diisocyanatesinclude, without limitation, m-phenylene diisocyanate, the isomers oftolylene diisocyanate including 2,4-tolylene diisocyanate and2,6-tolylene diisocyanate, mixtures of 2,4- and 2,6-tolylenediisocyanate, hexamethylene diisocyanate, tetramethylene diisocyanate,cyclohexane-1,4-diisocyanate, any of the isomers of hexahydrotolylenediisocyanate, isophorone diisocyanate, any of the isomers ofhydrogenated diphenylmethane diisocyanate includingmethylene-bis-4-cyclohexyl isocyanate, naphthylene-1,5-diisocyanate,1-methoxyphenyl-2,4-diisocyanate, any of the isomers of diphenylmethanediisocyanate, including 2,2′-diphenylmethane diisocyanate,2,4′-diphenylmethane diisocyanate, and 4,4′-diphenylmethanediisocyanate, isomers of biphenylene diisocyanate including 2,2′-,2,4′-, and 4.4′-biphenylene diisocyanates, 3,3′-dimethoxy-4,4′-biphenyldiisocyanate and 3,3′-dimethyl-diphenylmethane-4,4′-diisocyanate,isomers of tetramethylxylylene diisocyanate (TMXDI) including m-TMXDIand p-TMXDI, isomers of xylylene diisocyanate including p-xylylenediisocyanate and m-xylylene diisocyanate, butylene diisocyanate,1,2-diisocyanatopropane, 1,3-diisocyanatopropane, ethylene diisocyanate,and combinations thereof. In one embodiment, the diisocyanate includes adiphenylmethane diisocyanate or mixtures of isomers thereof.Polyisocyanates having more than two isocyanate groups such as1,2,4-benzene triisocyanate may be included at low levels, but it ispreferred to use only diisocyanates.

[0022] Preferably, the reaction mixture of the polyester diol and thediisocyanate or diisocyanates further includes one or more chainextender molecules that have two groups reactive with isocyanatefunctionality selected from active hydrogen-containing groups such asprimary amine groups, secondary amine groups, thiol groups, and hydroxygroups. The molecular weights of the chain extenders preferably rangefrom about 60 to about 400. Alcohols and amines are preferred. Usefulexamples of extender compounds include, without limitation, diols,dithiols, diamines, or compounds having a mixture of hydroxyl, thiol,and primary or secondary amine groups, such as aminoalcohols, aminoalkylmercaptans, and hydroxyalkyl mercaptans. Particular examples of suchmaterials include, without limitation, ethylene glycol, diethyleneglycol, and higher polyethylene glycol analogs like triethylene glycol;propylene glycol, dipropylene glycol, and higher polypropylene glycolanalogs like tripropylene glycol; 1,3-propanediol, 1,4-butanediol,1,3-butanediol, 1,6-hexanediol, 1,7-heptanediol, neopentyl glycol,dihydroxyalkylated aromatic compounds such as 4,4′-isopropylidenediphenol, (bisphenol A), resorcinol, catechol, hydroquinone,benzenedimethanols, the bis (2-hydroxyethyl) ethers of hydroquinone andresorcinol; p-xylene-α,α′-diol; the bis (2-hydroxyethyl) ether ofp-xylene-α,α′-diol; m-xylene-α,α′-diol and the bis (2-hydroxyethyl) andalkylene oxide adducts of such diols; diethyl toluene diamine,polyalkylpolyamines such as ethylenediamine, diethylenetriamine, andtriethylenetetramine, difunctional polyoxyalkylene amines (availablecommercially from BASF Corporation or from Huntsman under the trademarkJEFFAMINE®), methylenedianiline p-phenylenediamine, m-phenylenediamine,benzidine, 4,4′-methylene-bis (2-chloroaniline), alkanolamines andalkylalkanolamines such as ethanolamine, propanolamine, butanolamine,methylethanolamine, ethylethanolamine, methylpropanolamine,tert-butylaminoethanol, and combinations thereof. Preferred extendersinclude ethylene glycol, diethylene glycol, triethylene glycol,tetraethylene glycol, propylene glycol, dipropylene glycol, tripropyleneglycol, tetrapropylene glycol, 1,3-propylene glycol, 1,4-butanediol,1,6-hexanediol, and combinations of these. In addition to thedifunctional extenders, a small amount of trifunctional extenders suchas trimethylol propane, 1,2,6-hexanetriol and glycerol, and/ormonofunctional active hydrogen compounds such as butanol or dimethylamine, may also be present. The amount of trifunctional extenders and/ormonofunctional compounds employed is preferably 5.0 mole percent or lessbased on the total moles of active hydrogen reactants employed.

[0023] In general, the ratio of equivalents of polyisocyanate, which ispreferably all diisocyanate, to combined equivalents of polyester dioland extender ranges from about 0.96 to about 1.05 equivalent ofisocyanate to 1 equivalent of the combined polyester diol and extender.More preferred is a range of from about 0.98 to about 1.04 equivalentsof isocyanate per equivalent of combined polyester diol and extender andeven more preferred is a range of about 0.98 to about 1.02 equivalent ofisocyanate to 1 equivalent of the combined polyester diol and extenderto prepare the elastomeric polyurethane.

[0024] The thermoplastic polyurethane preferably has a weight averagemolecular weight of at least about 60,000, more preferably at leastabout 100,000. The thermoplastic elastomer also preferably has a weightaverage molecular weight of up to about 500,000, more preferably up toabout 300,000.

[0025] The thermoplastic polyurethane composition of the first layer isblended with at least one copolymer of ethylene and vinyl alcohol. Thecopolymer of ethylene and vinyl alcohol may be included in the blendedmaterial in an amount from about 1 to about 12 percent by weight.Preferred copolymers of ethylene and vinyl alcohol have an averageethylene content of an amount from about 25 mole percent to about 48mole percent. Particularly preferred are copolymers of ethylene andvinyl alcohol having a weight average molecular weight of at least about20,000, and preferably a weight average molecular weight of up to about50,000. Commercial products are available under the name SORANOL fromNippon Gohsei Co., Ltd. and under the trademark EVAL® from the EvalcaCompany (Lisle, Ill.), a subsidiary of Kuraray Co., Ltd. (Osaka, Japan).

[0026] The blend material can be prepared by combining at leastpartially virgin thermoplastic polyurethane and a recycled material ofthe copolymer of ethylene and vinyl alcohol. The recycled material maybe a laminate having a layer including the copolymer of ethylene andvinyl alcohol and a layer including a thermoplastic polyurethanematerial. The thermoplastic polyurethane material of the recycledmaterial preferably has the same composition as the thermoplasticpolyurethane composition with which the recycled material is blended.

[0027] The laminate membrane further includes a second layer including acopolymer of ethylene and vinyl alcohol. The second layer may alsoinclude other materials that serve to block the egress of fluid (gas orliquid) molecules through the membrane. Examples of such materialsinclude, without limitation, vinylidene chloride polymer; acrylonitrilepolymer; copolymers of acrylonitrile and methyl acrylate;semicrystalline polyesters, such as polyethylene terephthalate;polyamides, particularly semicrystalline nylons; crystalline polymers;epoxy resins, including resorcinol-based epoxy resins, amines such asN,N-dimethylethylenediamine (DMDEA), JEFFAMINE® 600, 3-amino-n-propanol,and 4-amino-n-butanol; polyurethane engineering thermoplastics, such asthe material available under the trademark ISOPLAST® from the DowChemical Company; and combinations of these materials. Preferably, thepolymeric barrier material of the barrier layer consists essentially ofethylene-vinyl alcohol copolymer.

[0028] The membrane may include further layers in addition to the first(blend) layer and the second (barrier) layer. In one embodiment, themembrane includes at least one third layer of a thermoplastic elastomer,preferably the thermoplastic polyurethane already described, that doesnot include the copolymer of ethylene and vinyl alcohol. In onepreferred embodiment, the membrane is formed with an inner layer (thesecond layer) of the barrier material composition adjacent on each sideto layers of thermoplastic elastomer (the third layers), the membranehaving exterior layers of the blend material (the first layers). Thebarrier (second) and elastomer (third) layers can be alternated inadditional layers as desired, for example as layers ofblend-elastomerbarrier-elastomer-barrier-elastomer-blend to makemulti-layer laminate membranes.

[0029] Each of the first (blend), second (barrier), and third(elastomer) layers may include one or more modifiers and additives,preferably in minor amount. Examples of such modifiers and additivesinclude, without limitation, plasticizers, light stabilizers, hydrolyticstabilizers, thermal stabilizers, brighteners, antioxidants, rheologymodifiers, organic anti-block compounds, fungicides, antimicrobials(including bacteriocides and the like), mold release agents, waxes suchas Montan esters or bisamide waxes, processing aids, and combinations ofthese. Tinted transparent membranes may be formed with transparentcolorants, such as dyes or transparent pigments. Special effects in thetransparent membrane, e.g. iridescence, may be achieved by using specialeffect pigments.

[0030] Examples of hydrolytic stabilizers include two commerciallyavailable carbodiimide based hydrolytic stabilizers known as STABAXOL Pand STABAXOL P-100, which are available from Rhein Chemie of Trenton,N.J. Other carbodiimide- or polycarbodiimide-based hydrolyticstabilizers or stabilizers based on epoxidized soy bean oil may beuseful. The total amount of hydrolytic stabilizer employed willgenerally be less than 5.0 wt. % of the total weight of the layer.

[0031] Plasticizers can be included for purposes of increasing theflexibility and durability of the final product as well as facilitatingthe processing of the material from a resinous form to a membrane orsheet. By way of example, and without intending to be limiting,plasticizers such as those based on butyl benzyl phthalate (which iscommercially available, e.g. as Santicizer 160 from Monsanto) haveproven to be particularly useful. Regardless of the plasticizer ormixture of plasticizers employed, the total amount of plasticizer, ifany, should generally be less than 20.0 wt. % of the total layer,preferably less than about 5% by weight of the total layer.

[0032] In a preferred method of forming the footwear of the invention, ascrap material containing both the thermoplastic polyurethane and acopolymer of ethylene and vinyl alcohol is blended into virginthermoplastic polyurethane. Regardless of how the blended material isproduced, the copolymer of ethylene and vinyl alcohol is included in theblended material in an amount of up to about 12 percent by weight,preferably up to about 5 percent by weight, based on the combinedweights of copolymer of ethylene and vinyl alcohol and thermoplasticpolyurethane. If prepared using scrap material having a layer of thethermoplastic polyurethane and a layer of the copolymer of ethylene andvinyl alcohol, the scrap material may be blended into the virginthermoplastic polyurethane by any of the methods available in the art.In one preferred method, the scrap material is first ground and then fedinto an extruder, either as a mixture along with pellets of the virginthermoplastic polyurethane or through a separate port from the virginthermoplastic polyurethane. The extruder may be a single screw or twinscrew extruder. The ground scrap material and the virgin thermoplasticpolyurethane are melt mixed in the extruder barrel and then extruded toform the first layer of the barrier membrane.

[0033] The layer of blended material of the membrane has a haze of up toabout 12%, preferably no more than about 10%, more preferably no morethan about 5% and still more preferably no more than about 1.5%. Thehaze of the membrane, having layers in addition to the blended material,in particular having a layer including the second layer with a copolymerof ethylene and vinyl alcohol, preferably has a haze of up to about 15%,preferably up to about 12%, and more preferably up to about 10%. Thehaze of the membrane or of the blended material may be measured by ASTMD-1003.

[0034] While the laminate membrane may be thin or thick, the laminatemembrane should be thick enough to provide adequate wall strength andyet thin enough to provide adequate flexibility. Laminate membranethicknesses from about 20 mils to about 70 mils are typical for blowmolding operations. In the preferred five-layer structure (firstlayer-third layer-second layer-third layer-first layer), it is desirablefor the barrier, second layer and the adjacent third, thermoplasticelastomer layer to each be at least about 0.4 mil thick, preferably atleast about 0.5 mil thick, more preferably at least about 0.6 mil thick,and still more preferably at least about 1 mil thick; and for each ofthese layers to be up to about 3 mils thick, preferably up to about 2.5mils thick, more preferably up to about 2 mils thick, and yet morepreferably up to about 1.6 mils thick. The first, blend layers arepreferably at least about 7 mils thick, more preferably at least about 8mils thick, and still more preferably at least about 9 mils thick; andpreferably up to about 20 mils thick, more preferably up to about 15mils thick.

[0035] The membranes have a tensile strength on the order of at leastabout 2500 psi; a 100% tensile modulus of between about 350-3000 psiand/or an elongation of at least about 250% to about 700%.

[0036] The laminate membrane may be formed into a bladder by a blowmolding process. In general, the bladders may be formed by a first stepof coextruding the layers, or plies, in a laminate film of flat ortubular shape, then blow molding the film or tube into a desired finalshape. For example, melt materials of the layers may be co-extruded as aparison. A mold having the desired overall shape and configuration ofthe bladder is in position to receive the parison and is closed aroundthe parison. The parison is cut at the edge of the mold. The mold ismoved back to a position away from the extrusion die. The open portionof the parison above the mold is then fitted with a blow tube throughwhich pressurized air or other gas, such as nitrogen, is provided. Thepressurized air forces the parison against the inner surfaces of themold. The material is hardened in the mold to form a bladder having thepreferred shape and configuration. The blown, shaped laminate is allowedto cool and harden in the mold, which may be at about 30° F. to 80° F.,before it is removed from the mold. Meanwhile, a new mold is moved intoplace to accept the next section from the parison that has been cut awayfrom the first mold.

[0037] Besides blow molding using continuous extrusion, the forming stepmay use intermittent extrusion by reciprocating screw systems, ramaccumulator-type systems, or accumulator head systems; co-injectionstretch blow molding; extruded or co-extruded sheet, blown film tubing,or profiles. Other forming methods include injection molding, vacuummolding, transfer molding, pressure forming, heat-sealing, casting, meltcasting, RF welding and so on.

[0038] The laminate may undergo further forming steps. For example, aflat laminate film may be cut into a desired shape. Two portions of theflat film may be sealed at the edges to form a bladder. The laminatefilm may alternatively be rolled into a tube and RF welded at the edgesto form a bladder.

[0039] The bladder may be inflated with a fluid, preferably a gas, andpermanently sealed. The durable, elastomeric membranes of the inflatedbladders are incorporated into the sole of an article of footwear, forexample as shown in FIG. 1. By “durable” it is meant that the membranehas excellent resistance to fatigue failure, which means that themembrane can undergo repeated flexing and/or deformation and recoverwithout delamination along the layer interfaces of composite barriermembranes, preferably over a broad range of temperatures.

[0040] Footwear, and in particular shoes, usually include two majorcomponents: a shoe upper and a sole. The general purpose of the shoeupper is to snugly and comfortably enclose the foot. Ideally, the shoeupper should be made from an attractive, highly durable, comfortablematerials or combination of materials. The sole, constructed from adurable material, is designed to provide traction and to protect thefoot during use. The sole also typically serves the important functionof providing enhanced cushioning and shock absorption during athleticactivities to protect the feet, ankles, and legs of the wearer from theconsiderable forces generated. The force of impact generated duringrunning activities can amount to two or three times the body weight ofthe wearer, while other athletic activities such as playing basketballmay generate forces of between six and ten times the body weight of thewearer. To provide these functions, the sole typically has a midsole orinsole having cushioning and an outsole having a traction surface. Thebladder preferably is applied to the insole portion of a shoe, which isgenerally defined as the portion of the shoe upper directly underlyingthe plantar surface of the foot.

[0041] The membranes preferably are capable of containing a captive gasfor a relatively long period of time. In a highly preferred embodiment,for example, the membrane should not lose more than about 20% of theinitial inflated gas pressure over a period of approximately two years.In other words, products inflated initially to a steady state pressureof between 20.0 to 22.0 psi should retain pressure in the range of about16.0 to 18.0 psi for at least about two years.

[0042] The bladder may be inflated with air or components of air such asnitrogen, or with supergases, preferably with nitrogen, to an internalpressure of at least about 3 psi, preferably at least about 5 psi, andup to about 50 psi. Preferably the bladder is inflated to an internalpressure from about 5 psi to about 35 psi, more preferably from about 5psi to about 30 psi, still more preferably from about 10 psi to about 30psi, and yet more preferably from about 10 psi to about 25 psi. Afterbeing inflated, the inflation port may be sealed, for example by RFwelding, for a permanently sealed inflated bladder.

[0043] For the bladders to remain permanently inflated, the gastransmission rate must be suitably low. In one preferred embodiment, themembrane of the bladder has a gas transmission rate toward theinflationary gas, which is preferably air or nitrogen gas, should beless than about 15 cubic centimeters per square meter per atmosphere perday (cc/m²·atm·day), preferably less than about 6 cc/m²·atm·day,particularly less than about 4 cc/m²·atm·day, more preferably less thanabout 2.5 cc/m²·atm·day, yet more preferably less than about 1.5cc/m²·atm·day, and particularly preferably less than about 1cc/m²·atm·day. An accepted method of measuring the relative permeance,permeability, and diffusion of different film materials is set forth inthe procedure designated as ASTM D-1434. While nitrogen gas is thepreferred captive gas for many embodiments and serves as a benchmark foranalyzing gas transmission rates in accordance with ASTM D-1434, themembranes can contain a variety of different gases and/or liquids.

[0044] The invention is further described in the following example. Theexamples are merely illustrative and do not in any way limit the scopeof the invention as described and claimed. All parts are parts by weightunless otherwise noted.

EXAMPLE 1

[0045] A dry blend of 80 parts by weight of a ground scrap material (10%by weight of copolymer of ethylene and vinyl alcohol, 90% by weight of apolyurethane based on poly(butanediol adipate)) and 20 parts by weightof virgin polyurethane having the same composition as the polyurethaneof the scrap material was melt mixed using a twin screw extruder. Thematerial was extruded and blow molded into a five-layer parison havinglayers A-B-C-B-A, with the A layers being of the blend, the B layersbeing of the polyurethane based on poly(butanediol adipate), and the Clayer being of copolymer of ethylene and vinyl alcohol. The A layerswere approximately 25 mils thick, the B layers approximately 2 milsthick, and the C layer approximately 0.7 mil thick.

[0046] The haze of the sample was measured and normalized to a value fora 20 mil sample of less than 12%.

[0047] The invention has been described in detail with reference topreferred embodiments thereof. It should be understood, however, thatvariations and modifications can be made within the spirit and scope ofthe invention.

What is claimed is:
 1. An article of footwear, comprising an upper and a sole attached to said upper, said sole comprising a fluid-filled bladder comprising a laminate membrane, wherein said laminate membrane comprises at least a first layer comprising a thermoplastic polyurethane and a copolymer of ethylene and vinyl alcohol , wherein said thermoplastic polyurethane includes at least about 50 mole percent, based on the total moles of hydroxyl-functional reactants used to produce the polyurethane, of a polyester diol having a weight average molecular weight of at least about 500 and having a linear alkylene group having from two to about six carbon atoms between substantially all of the ester groups and a second layer comprising a copolymer of ethylene and vinyl alcohol; wherein at least a part of said membrane forms at least a part of an exterior portion of said sole.
 2. An article of footwear according to claim 1, wherein the first layer has a haze of not more than about 12%.
 3. An article of footwear according to claim 1, wherein the first layer has a haze of not more than about 5%.
 4. An article of footwear according to claim 1, wherein the membrane includes a dye or tansparent pigment.
 5. An article of footwear according to claim 1, wherein the fluid comprises a member selected from the group consisting of air, nitrogen, supergases, and combinations thereof.
 6. An article of footwear according to claim 1, wherein the fluid is colored.
 7. An article of footwear according to claim 1, wherein the first layer is an outer layer of the membrane.
 8. An article of footwear according to claim 1, wherein the bladder is permanently sealed.
 9. An article of footwear according to claim 1, wherein the membrane has a gas transmision rate, normalized for a 20-mil membrane thickness, of less than about 1(cc)(20mils)/(m²)(24 hours).
 10. An article of footwear according to claim 1, wherein the thermoplastic polyurethane includes at least about 62 mole percent, based on the total moles of hydroxyl-functional reactants used to produce the polyurethane, of the polyester diol.
 11. An article of footwear according to claim 1, wherein the polyester diol is a lactone-based.
 12. An article of footwear according to claim 1, wherein the polyester diol is a poly(epsilon caprolactone) diol.
 13. An article of footwear according to claim 12, wherein the poly(epsilon caprolactone) diol has a weight average molecular weight from about 1500 to about
 3000. 14. An article of footwear according to claim 12, wherein the poly(epsilon caprolactone) diol has a weight average molecular weight from about 1800 to about
 2500. 15. An article of footwear according to claim 1, wherein the polyester diol has a weight average molecular weight of at least about
 1000. 16. An article of footwear according to claim 1, wherein the polyester diol has a weight average molecular weight from about 1000 to about
 5000. 17. An article of footwear according to claim 1, wherein the thermoplastic polyurethane is formed by reaction of a mixture comprising a member selected from the group consisting of diphenylmethane diisocyanate and mixtures of isomers thereof.
 18. An article of footwear according to claim 1, wherein the thermoplastic polyurethane is formed by reaction of a mixture comprising one or more chain extenders having two groups reactive with isocyaante functionality having molecular weight from about 60 to about
 400. 19. An article of footwear according to claim 18, wherein the one or more chain extenders are selected from the group consisting of alcohols, amines, and combinations thereof.
 19. An article of footwear according to claim 18, wherein the one or more chain extenders are selected from the group consisting of ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, propylene glycol, dipropylene glycol, tripropylene glycol, tetrapropylene glycol, 1,3-propylene glycol, 1,4-butanediol, 1,6-hexanediol, and combinations thereof.
 20. An article of footwear according to claim 18, wherein the one or more chain extenders are employed in an amount of up to about 5.0 mole percent, based on the total moles of active hydrogen reactants.
 21. An article of footwear according to claim 1, wherein said thermoplastic polyurethane has a weight average molecular weight of at least about 60,000.
 22. An article of footwear according to claim 1, wherein said thermoplastic polyurethane has a weight average molecular weight from about 100,000 to about 500,000.
 23. An article of footwear according to claim 1, wherein the first layer includes from about 1 to about 12 percent by weight of the copolymer of ethylene and vinyl alcohol.
 24. An article of footwear according to claim 1, wherein the copolymer of ethylene and vinyl alcohol of the first layer has an average ethylene content from about 25 mole percent to about 48 mole percent.
 25. An article of footwear according to claim 1, wherein the copolymer of ethylene and vinyl alcohol of the first layer has a weight average molecular weight from about 20,000 to about 50,000.
 26. An article of footwear according to claim 1, wherein the second layer further comprises a member selected from the group consisting of vinylidene chloride polymer acrylonitrile polymer, copolymers of acrylonitrile and methyl acrylate, semicrystalline polyesters, polyamides, semicrystalline nylons, crystalline polymers, epoxy resins, resorcinol-based epoxy resins, polyurethane engineering thermoplastics, and combinations thereof.
 27. An article of footwear according to claim 1, wherein the laminate membrane comprises a third layer, wherein the third layer comprises a thermoplastic elastomer.
 28. An article of footwear according to claim 27, wherein the third layer consists essentially of a thermoplastic polyurethane and a copolymer of ethylene and vinyl alcohol , wherein said thermoplastic polyurethane includes at least about 50 mole percent, based on the total moles of hydroxyl-functional reactants used to produce the polyurethane, of a polyester diol having a weight average molecular weight of at least about 500 and having a linear alkylene group having from two to about six carbon atoms between substantially all of the ester groups.
 29. An article of footwear according to claim 28, wherein the laminate membrane has the second layer as an inner layer, the third layer adjacent to the second layer on one side and a fourth layer having the composition of the third layer adjacent to the second layer on the other side, and the first layer and a fifth layer having the composition of the first layer as outermost layers.
 30. An article of footwear according to claim 1, wherein the bladder has an internal pressure from about 5 to about 35 pounds per square inch.
 31. A method of manufacturing articles of footwear, comprising steps of: (a) manufacturing a laminate membrane comprising a first layer comprising a thermoplastic polyurethane, wherein said thermoplastic polyurethane includes at least about 50 mole percent, based on the total moles of hydroxyl-functional reactants used to produce the polyurethane, of a polyester diol having a weight average molecular weight of at least about 500 and having a linear alkylene group having from two to about six carbon atoms between substantially all of the ester groups and a second layer comprising a copolymer of ethylene and vinyl alcohol, (b) forming the laminate membrane into a sealed, fluid-filled bladder; and (c) including the bladder in a shoe, wherein at least a part of said membrane forms an exterior part of said shoe, wherein scrap material having said first and second layers is generated during steps (a)-(c); (d) including said scrap material in said manufacturing step (a) by blending said scrap material into said first layer to produce a layer of blended material.
 32. A method according to claim 31, wherein the layer of blended material has a haze of not more than about 12%.
 33. A method according to claim 31, wherein the layer of blended material has a haze of not more than about 5%.
 34. A method according to claim 31, wherein the fluid comprises a member selected from the group consisting of air, nitrogen, supergases, and combinations thereof.
 35. A method according to claim 31, wherein the layer of blended material is an outer layer of the membrane.
 36. A method according to claim 31, wherein the membrane has a gas transmision rate, normalized for a 20-mil membrane thickness, of less than about 1(cc)(20mils)/(m²)(24 hours).
 37. A method according to claim 31, wherein the polyester diol is a poly(epsilon caprolactone) diol.
 38. A method according to claim 37, wherein the poly(epsilon caprolactone) diol has a weight average molecular weight from about 1500 to about
 3000. 39. A method according to claim 31, wherein the thermoplastic polyurethane is formed by reaction of a mixture comprising a member selected from the group consisting of diphenylmethane diisocyanate and mixtures of isomers thereof.
 40. A method according to claim 31, wherein the thermoplastic polyurethane is formed by reaction of one or more chain extenders employed in an amount of up to about 5.0 mole percent , based on the total moles of active hydrogen reactants.
 41. A method according to claim 31, wherein said thermoplastic polyurethane has a weight average molecular weight of at least about 60,000.
 42. A method according to claim 31, wherein said thermoplastic polyurethane has a weight average molecular weight from about 100,000 to about 500,000.
 43. A method according to claim 31, wherein the layer of blended material includes from about 1 to about 12 percent by weight of the copolymer of ethylene and vinyl alcohol.
 44. A method according to claim 31, wherein the copolymer of ethylene and vinyl alcohol has an average ethylene content from about 25 mole percent to about 48 mole percent.
 45. A method according to claim 31, wherein the copolymer of ethylene and vinyl alcohol has a weight average molecular weight from about 20,000 to about 50,000.
 46. A method according to claim 31, wherein the laminate membrane has the second layer as an inner layer, the first layer adjacent to the second layer on one side and a fourth layer having the composition of the first layer adjacent to the second layer on the other side, and the layer of blended material and a fifth layer having the composition of the layer of blended material as outermost layers. 